John H. Comtois

Use of micro-electro-mechanical deformable mirrors to control aberrations in optical systems: theoretical and experimental results

Micro-electro-mechanical deformable mirrors (MEM-DMs) are solid-state electronic devices with small, movable reflective surface elements that can be used to manipulate the phase of optical wavefronts. MEM-DMs differ from more conventional continuous-facesheet deformable mirrors in that the movable surface of a MEM-DM consists of a set of segmented moving surfaces. The segmented, reflective surfaces of a MEM-DM give rise to larger diffraction effects than those provided by continuous-facesheet deformable mirrors. However, MEM-DMs are still attractive due to their low cost and the low drive voltages. We explore the theoretical limits of performance of MEM-DMs for controlling fixed aberrations in optical systems, and we present laboratory results demonstrating reduction of a fixed aberration using a MEM-DM device. Results presented here show that while a MEM-DM does provide some degree of aberration control, diffraction effects arising from the static support structures of the MEM-DM surface are significant. An alternative design that uses a lenslet array in conjunction with the MEM-DM is shown through theoretical studies to provide superior aberration correction with lower residual effects due to diffraction.

Multichip module packaging of microelectromechanical systems

Abstract Methods of packaging microelectromechanical systems (MEMS) using two advanced multichip module (MCM) foundry processes are described. Special-purpose surface and bulk micromachined MEMS packaging test dies were designed and fabricated. The MEMS test dies were successfully packaged with CMOS electronics dies using the ‘chips first’ General Electric high-density interconnect (HDI) technology. Methods for reducing the potential for laser-induced damage and residue formation in the HDI process are demonstrated. The micro module systems MCM-D process was also successfully investigated for applicability to MEMS packaging. Development of MEMS compatible MCM packaging provides an alternative to monolithic fabrication for integration of MEMS and microelectronics.

Surface-micromachined polysilicon MOEMS for adaptive optics

Abstract This paper presents an overview of Air Force research and development programs in micro-opto-electro-mechanical systems (MOEMS) for adaptive optics using commercially available surface-micromachined polysilicon fabrication processes. Adaptive optic systems are a growing area of interest because advanced technologies are now becoming available to make these systems lightweight, low power, and compact. In short, they are becoming practical for space, missile, and man-portable applications. The technologies that are making this possible include highly integrated low power electronics, new processing architectures for error sensing and control, flexible high density packaging, and especially MOEMS. Micromirror design, mirror array design, and design tradeoffs are discussed, as well as high density packaging for combining MEMS-specific die with standard electronic die. The micromirror devices described below were developed for adaptive optic systems, and for exploring the design, manufacture, and actuation options made possible by the commercial surface-micromachining fabrication processes.

MOEMS for adaptive optics

This paper presents an overview of research and development programs at AFRL/VS in micro-opto-electro-mechanical systems (MOEMS) for adaptive optics. Adaptive optic systems typically consist of a wavefront phase sensor, focusing optics, a spatial light modulator (SLM) for correcting phase errors, imaging sensors, and the control and processing electronics. These systems have a simple purpose: they improve image quality by reducing the phase aberrations introduced when the wavefront travels through turbulent atmosphere or aberrations introduced by the optical system itself. As will be shown, aberration correction and controllable focus can also enable new system functions. Adaptive optic systems are becoming practical for space, missile, and man-portable applications. Comparisons are made between current macro-optical aberration correction systems and the micromirror based systems currently under development. These comparisons show how micromirrors are the crucial enabling technology for compacting these systems down to a size where their use in space can be contemplated. As an example of a space application, a proposed star tracker system is used as an example of a complete micro-optical system that employs not only a micromirror based SLM, but also a novel wavefront sensor, analog processing electronics, and new sensor electronics. Research on surface-micromachined polycrystalline silicon micromirrors will be reported, including work on several fabrication technologies for piston micromirrors and also for highly advanced micromirrors with tilting as well as piston motion. Design techniques for both individual micromirrors and arrays of micromirrors will be detailed for both the most advanced of these processes, the Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT) process, and for the most widely available process, the Multi-User MEMS Process (MUMPS). Results of characterization testing and device modeling will be presented to show the advantages of each of the various design approaches.

Design and simulation of advanced surface micromachined micromirror devices for telescope adaptive optics applictions

This paper describes the design, fabrication, modeling, surface characterization, and simulation of advanced surface micromachined micromirror devices that are optimized for adaptive optics applications. Design considerations and fabrication capabilities are presented. Simulation of adaptive optics performance of unique Flexure-Beam and Axial-Rotation Micromirror devices is performed for many common aberrations. These devices are fabricated in the state-of-the-art four-level planarized polysilicon process available at Sandia National Laboratories known as the Sandia Ultra-planar Multi-level planarized MEMS Technology. This enabling process permits the development of micromirror devices with near-ideal characteristics that have previously been unrealizable in standard three-layer polysilicon processes. This paper describes such characteristics as elevated address electrodes, array wiring techniques, planarized mirror surfaces using chemical mechanical polishing, unique post-process metallization, and the best active surface area to date.

Development of advanced second-generation micromirror devices fabricated in a four-level planarized surface-micromachined polycrystalline silicon process

This paper describes the design and characterization of several types of micromirror devices to include process capabilities, device modeling, and test data resulting in deflection versus applied potential curves and surface contour measurements. These devices are the first to be fabricated in the state-of-the-art four-level planarized polysilicon process available at Sandia National Laboratories known as the Sandia Ultra-planar Multi-level MEMS Technology. This enabling process permits the development of micromirror devices with near-ideal characteristics which have previously been unrealizable in standard three-layer polysilicon processes. This paper describes such characteristics which have previously been unrealizable in standard three-layer polysilicon processes. This paper describes such characteristics as elevated address electrodes, various address wiring techniques, planarized mirror surfaces suing Chemical Mechanical Polishing, unique post-process metallization, and the best active surface area to date.

Design and fabrication of optical MEMS using a four-level planarized surface-micromachined polycrystalline silicon process

This paper describes the design and fabrication of optical microelectromechanical systems devices using the Sandia Ultra-planar Multi-level MEMS Technology fabrication process. This state-of-the-art process, offered by Sandia National Laboratories, provides unique and very advantageous features which make it ideal for optical devices such as micromirrors. This enabling process permits the development of micromirror devices with near-ideal characteristics which have previously been unrealizable in standard polysilicon processes. This paper describes many of these characteristics such as elevated address electrodes, various address wiring techniques, planarized mirror surfaces using Chemical Mechanical Polishing, unique post-process metallization, and the best active surface area to date.

Design and testing of polysilicon surface-micromachined piston micromirror arrays

THis paper presents optical testing of polysilicon surface micromachined piston micromirror arrays. Similar piston micromirror arrays were fabricated using two different commercially available surface micromachining foundry processes: the DARPA supported multi-user MEMS processes (MUMPs), and Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT). All test arrays employ square reflecting elements in an 8 X 8 element 203 micrometers square grid. Fabrication constraints limit the MUMPs designs to fill-factors of less than 80 percent. The chemical mechanical polishing planarization step integral to the SUMMiT process allows an as-drawn fill-factor of 95 percent to be easily achieved. MUMPs designs employ both the standard gold metallization and maskless sputtered chromium/gold post-process metallization, while post process metallization is the only option for the SUMMiT design. Testing of the micromirror arrays focuses on microscope interferometer characterization of mirror topography, and measurement of the far field diffraction pattern for each. The measured results show that control of the individual micromirror element surface topography is more important for imaging applications than maximizing the as-drawn fill-factor.

Extension of high density interconnect multichip module technology for MEMS packaging

In this paper, we describe research into extending the General Electric chip-on-flex (COF) process for packaging microelectromechanical systems (MEMS). COF is a derivative of the high density interconnect (HDI) used for multichip module packaging of microelectronics. COF is a high performance, low cost multichip packaging technology in which die are encased in a molded plastic substrate and interconnects are made via a thin-film structure formed over the components. For MEMS packaging, the standard COF process has been modified to include laser ablating windows in the interconnect overlay to allow access to MEMS. Special purpose surface and bulk micromachining test die were developed and packaged with CMOS electronics using the COF process. The COF/MEMS packaging technology is well-suited for applications in which monolithic integration of MEMS and electronics is not optimal.

Radiation-induced effects research in emerging photonic technologies: vertical cavity surface emitting lasers, GaN light-emitting diodes, and microelectromechanical devices

High quality optical fiber to OEIC pigtailing, using non-conventional technology, is required to create a real integrated optical system for optical communications, computing, signal processing, control, and sensing. In this paper, Physical Optics Corporation (POC) presents a novel singlemode fiber to singlemode GaAs channel waveguide pigtailing approach. This pigtailing approach involves two key technologies. First, a fiber end-face lensing technology was used to improve modeprofile matching between singlemode fiber and singlemode channel waveguide, so fiber to waveguide coupling efficiency could be improved. Second, resistance layer assisted dual-carrier-soldering (RLADCS) technology was introduced to facilitate fiber and waveguide chip alignment and fixing, so accurate, convenient, and reliable fiber to optoelectronic integrated cicuit (OEIC) pigtailing could be achieved. By using radiation hardened fiber and special OEIC, this pigtailing and packaging technology has potential applications in a space environment. This publication addresses all aspects of this pigtailing approach, including theoretical analysis, design, fabrication, testing, and measurement results.